The incidence of amenorrhea among female athletes is much greater than that of the general population. As a large percentage of these amenorrheic athletes are vegetarians, and consumption of a vegetarian diet has been shown to alter menstrual cyclicity, the purpose of this investigation is to determine if consumption of a vegetarian diet and/or performance of physical activity alters menstrual cyclicity in previously sedentary women. A hormonal profile (FSH, LH, estradiol and progesterone) of a group of nonvegetarian regularly menstruating sedentary women (n=48) will be obtained for one control menstrual cycle. One half of the subjects will then be randomly selected and will consume a vegetarian diet (no animal products except for small amounts of cheese and milk) for three consecutive months, while the other half of the subjects will maintain their regular dietary habits. One half of the subjects from each of the diet groups will also perform physical activity for up to 60?minutes per day, six days per week, for the three months. During the third month of the dietary/physical activity treatment a second hormonal profile will be obtained on each subject. The subjects menstrual cycles will then be examined for any hormonal alterations which lead or could lead to menstrual cycle irregularities. If dietary manipulation can be shown to affect the menstrual rhythmicity of sedentary and physically active women, then a case can be made for altering the dietary habits of female athletes to protect against lower bone density and higher serum low density lipoprotein cholesterol levels found in amenorrheic runners.